Engine exhaust filters can have a variety of constructions. One type of exhaust filter includes a cellular ceramic core defining a honeycomb of channels having plugged ends. Filters having this construction are disclosed in U.S. Pat. Nos. 4,276,071 and 4,851,015. Other exhaust filters include a filter media defined by a plug of wire mesh. Filters having this construction are disclosed in U.S. Pat. Nos. 3,499,269 and 4,902,487. Filters of the type indicated above can be catalyzed or un-catalyzed. Un-catalyzed filters require high temperatures to be efficiently regenerated. Catalyzed filters can be regenerated at lower temperatures, but can generate undesirable by-products such as NO2.
Filters are also often used to filter the intake air drawn into an engine. U.S. Pat. Nos. 3,078,650 and 5,547,480 disclose air filters of the type used with the intake systems of engines. These filters include cylindrical pleated filter elements mounted within housings. The filter elements define hollow interiors, and the air being filtered travels radially through the pleated filter elements. While suitable for engine intake applications, these types of filters are not adapted for the high temperature environment created by engine exhaust.
Engine emission regulations have become increasingly stringent. What are needed are alternative filtration systems for use in reducing engine exhaust emissions.